1. Field of the Invention
The present invention relates to a control apparatus of a hydraulic valve for holding load capable of precluding momentary drop of load drop in a hydraulic actuator such as a boom cylinder, etc. for thereby effectively preventing drop of load, and in particular to a control apparatus of a hydraulic valve for holding load in which a drain line of a holding valve adapted to preclude momentary drop of load in a hydraulic actuator is substituted with a path formed in the interior of a directional control valve, so that a pipe line of a drain side functioning as a hydraulic hose and exposed to the outside is not needed in the present invention.
2. Description of the Background Art
As shown in FIGS. 1 and 2, a control apparatus of a hydraulic valve for holding load in a conventional art includes a hydraulic pump 19 and a pilot pump 2 connected to an engine (not shown), a hydraulic actuator (not shown) connected to the hydraulic pump 19 like a boom cylinder, etc., a directional control valve 35 disposed in a flow path between the hydraulic pump 19 and the actuator and controlling a start, stop and direction change of the actuator by a spool 14 that is switched when pilot pressure is applied, a remote control valve (RCV) 1 adapted to supply pilot pressure to the directional control valve 35, a poppet 9 disposed in a flow path between the directional control valve 35 and the actuator and adapted to preclude momentary drop of load in the actuator, and a holding valve 20 connected to a side of a downstream of the poppet 9 and adapted to release upheld load of the actuator by a sub-spool 7 that is switched when pilot pressure is applied.
In the drawings, reference characters A and B represent a flow path connected to the actuator, respectively.
In the case that the spool 14 installed in the directional control valve 35 is at a neutral position (as shown in FIG. 1), a high pressure hydraulic fluid from the hydraulic actuator sequentially flows to a back chamber 10 through a port 12 formed in a holding valve block 18 and a through hole 11 formed in the poppet 9. The flow of the hydraulic fluid is blocked by the sub-spool 7, which is installed in the holding valve 20, and maintains a neutral position.
The poppet 9 is downwardly pressurized due to a difference in a cross section area of the poppet 9 as shown in FIG. 2, so that the hydraulic fluid from the actuator is prevented from being drained into a hydraulic tank, whereby load of an actuator is temporarily prevented from being dropped for thus implementing a holding function.
In the case that it is intended to release holding load function of the actuator, the remote control valve 1 is operated in the direction “b”, so that pilot pressure Pb discharged from the pilot pump 2 is introduced into the port of a spool cap 5 engaged in a left end of the directional control valve 35 through the pilot line 4, whereby the inner spool 14 is switched in the right direction shown in FIG. 2.
At the same time, the pilot signal pressure Pb flows through a pilot line 6 divided from the pilot line 4 and enables the sub-spool 7 installed in the holding valve 20 to be switched in the left direction shown in FIG. 2.
At this time, hydraulic fluid of high pressure in the back chamber 10 of the holding valve block 18 is drained to the hydraulic tank 3 through the drain line 8.
As the pressure of the hydraulic fluid of the back chamber 10 is dropped to the pressure of the hydraulic tank, a high load pressure from the actuator enables the poppet 9 to be upwardly moved as shown in FIG. 2 and is fed back to the hydraulic tank through a notch 15 of the spool 14, of which the position is switched, and a return line 16. The load holding function of the hydraulic actuator is released, and the actuator slowly moves downward.
In the control apparatus of a hydraulic valve for holding load in the conventional art, the pilot line 6 adapted to supply pilot pressure to the holding valve 20 for switching the sub-spool 7 and the drain line adapted to drain the hydraulic fluid of the back chamber 120 to the hydraulic tank 3 when the sub-spool 7 is switched are exposed to the outside with the shape of hydraulic hoses and are longitudinally connected.
In the conventional art, as the hydraulic hoses are exposed to the outside, the fabrication cost is increased. The length of the hydraulic hoses of the drain line 8 is increased, so that a backpressure is formed in the drain line. Therefore, the response time is decreased during the operation of the remote control valve 1, so that it is difficult to control the equipment.